This invention relates to a gate valve with improved seals to the annular seat elements.
The invention provides an improved gate valve of the slab gate valve type which includes floating annular seat elements sealed in counterbores or seat pockets in the flowbore of the valve body. Gate valves of this nature, the problems inherent with fines entering the sealing areas of these gate valves, and the prior art efforts to solve these problems are well reviewed in prior art patents, see for example U.S. Pat. Nos. 4,645,179; 5,029,812; and 5,727,775.
In the slab gate valve design, tight clearances and metal-to-metal sealing surfaces are maintained between the valve body (i.e., seat pockets with optional metal carrier rings), the annular seat element and the gate. However tight the clearances are, gaps exist between all surfaces. The upstream annular seat element (at the inlet) and the gate float downstream (toward the outlet) with the pressure to seal against the downstream annular seat element. Particles smaller than the gap between the sealing surfaces may enter the gap. In most cases, the gate valves are expected to flow in one direction and hold pressure in the opposite direction. Over time, particles can get in between all surfaces and eventually produce leakage.